1. Field of the Invention
The invention relates to the field of high-speed optical communications and to a plastic optical fiber used therefor. The invention concerns in particular a connecting structure between the plastic optical fiber and a light-receiving element.
2. Description of the Prior Art
A plastic optical fiber, in general, has a wider core diameter than quartz-type optical fibers. It is therefore easy to connect plastic optical fibers to one another or to another optical element. Also, the components of the plastic optical fiber are not required to have a precise dimension. The plastic optical fiber is therefore useful for a cost-effective optical communications device, the optical alignment of which can easily be performed.
In the past, when optical communications were transmitted at a relatively slow speed, a plastic optical device was generally configured such than an end surface of the plastic optical fiber was disposed face-to-face against the light-receiving face of an optical element such as photo-diode.
However, as recent research has progressed into high-speed communications using a plastic optical fiber, there arose the problem of connection between the fiber and an optical receptor.
The response speed of a photo-diode is determined by the time span, during which the electrons, that are excited by the light entering its light-receiving portion through the light-receiving face, reach its inside electrode. In order to obtain a response speed applicable to high-speed optical communications in excess of several hundreds of Mbps, the light-receiving portion of the photo-diode has to be scaled down, so that the above-mentioned time span is shortened.
On the other hand, when the light-receiving portion is small, only a part of the light emitted from the end face of a plastic optical fiber is received therethrough, resulting in a high connection loss between the fiber and the photo-diode. The end face of a plastic optical fiber is at the end of the plastic optical fiber that faces the light-receiving portion.